As a conventional system for parallelly driving an arm member by two actuators, there are a system that includes a position detector in each of master and slave actuators, and a system that does not include a position detector in one of the actuators.
FIG. 9 shows an example of a conventional parallel drive system. FIG. 9(a) is a configuration diagram of a parallel drive system that includes a position detector only in a master actuator. In FIG. 9(a), movable units 5A and 5B of respective master and slave actuators are connected to each other by an arm member 8 that includes a head 9. A master servo amplifier 12A executes position control based on a position instruction received from a controller 14 and on master position information that is inputted thereto from a position detector 10 and indicates a position of the movable unit 5A of the master actuator. The master servo amplifier 12A transmits a torque instruction to a slave servo amplifier 12B, and the slave servo amplifier 12B executes torque control using the torque instruction, thus establishing the parallel drive system (see, for example, Patent Literature 1).
FIG. 9(b) is a diagram showing another conventional parallel drive system. In FIG. 9(b), master and slave actuators include their respective position detectors 10A and 10B. The master and slave servo amplifiers 12A and 12B execute position control based on a position instruction received from the controller 14 and position information that is inputted from the position detectors 10A and 10B and indicates positions of the movable units 5A and 5B. Furthermore, in the system shown in FIG. 9(b), position information pieces obtained by the position detectors 10A and 10B are also inputted to the slave and master servo amplifiers 12B and 12A, respectively, as represented by broken-line arrows, thereby to share the position information pieces between the amplifiers 12A and 12B. By executing control to suppress a difference in a position deviation between the movable units of the actuators, or control to move the positions of the movable units of the master and slave movable units more synchronously with each other in the servo amplifier, the parallel drive system that can maintain the parallelism of the arm member is established (see, for example, Patent Literature 2).